The role of intestinal nematode infections in the aetiology of iron deficiency and anaemia in pregnant women was investigated in peri-urban and rural areas of Western Sierra Leone. A randomised placebo-controlled field trial was carried out to evaluate the efficacy of a single course of albendazole (400 mg) and daily iron-folate supplements (36 g iron and 5 mg folate), administered after the first trimester, as control interventions for intestinal nematode infections and anaemia during pregnancy. At baseline, in the first trimester of pregnancy, the prevalence (and geometric mean intensity) of intestinal nematodes was as follows: Ascaris lumbricoides 21.1% (267 eggs per gram); Necator americanus 66.5% (191 epg); and Trichuris trichiura 71.9% (93 epg). Chronic undernutrition (height < 150 cm) and chronic energy deficiency (body mass index < 18.5 kg/m2) was found in 5.4% and 8.2% of women respectively. Anaemia (Hb < 110 g/l) was diagnosed in 58.7% of women and associated with iron deficiency (serum ferritin < 20 μg/l) in 21.2% of women. Iron deficiency is likely to have a dietary basis in these women. The dietary iron intake was predominantly non-haem, and was estimated to supply less than 1 g of absorbable iron daily. High fertility and closely spaced pregnancies placed additional stress on iron stores. The findings of this study indicate that anthelminthic treatment should be included in strategies to control maternal anaemia in Western Sierra Leone. It is recommended that pregnant women routinely receive a single course of anthelminthics after the first trimester, alongside daily iron-folate supplements, to minimise the decline in maternal Hb concentration during pregnancy. These interventions could be implemented through the existing primary health care system, although the use of traditional birth attendants should be investigated as a means of improving compliance and coverage. The implications of these findings for public health policy in other antenatal populations will depend on the local epidemiology of intestinal nematode infections and on the extent of underlying maternal iron deficiency and anaemia.